Method and apparatus for enhanced contention based random access procedure

ABSTRACT

A communication method and system for converging a fifth generation (5G) communication system for supporting higher data rates beyond a fourth generation (4G) system with a technology for Internet of things (IoT) are provided. The communication method and system may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method of a user equipment (UE) for performing a random access (RA) procedure is provided. The method includes transmitting a first message including a RA preamble and a UE identifier (ID) to a base station (BS), and receiving a second message including a sequence index of the RA preamble from the BS.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. § 119(e) of a U.S.provisional application filed on Oct. 7, 2016 in the U.S. Patent andTrademark Office and assigned Ser. No. 62/405,555, the entire disclosureof which is hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a method and an apparatus for acontention based random access (RA) procedure. More particularly, thepresent disclosure relates to a method and an apparatus for performing atwo-step contention based RA procedure and fall back between two-stepand four-step contention based RA procedures.

BACKGROUND

To meet the demand for wireless data traffic having increased sincedeployment of fourth generation (4G) communication systems, efforts havebeen made to develop an improved fifth generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘beyond 4G network’ or a ‘post long term evolution(LTE) system’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, beamforming, massivemultiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO),array antenna, analog beam forming, and large scale antenna techniquesare discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud radio access networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,coordinated multi-points (CoMP), reception-end interference cancellationand the like. In the 5G system, hybrid frequency shift keying (FSK) andquadrature amplitude modulation (QAM) modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), filter bank multi carrier (FBMC), non-orthogonal multiple access(NOMA), and sparse code multiple access (SCMA) as an advanced accesstechnology have been developed.

In the recent years several broadband wireless technologies have beendeveloped to meet the growing number of broadband subscribers and toprovide more and better applications and services. The second generation(2G) wireless communication system has been developed to provide voiceservices while ensuring the mobility of users. The third generation (3G)wireless communication system supports not only the voice service butalso data service. The 4G wireless communication system has beendeveloped to provide high-speed data service. However, the 4G wirelesscommunication system currently suffers from lack of resources to meetthe growing demand for high speed data services. Therefore, the 5Gwireless communication system is being developed to meet the growingdemand of various services with diverse requirements, e.g., high speeddata services, ultra-reliability and low latency applications andmassive machine type communication.

In existing wireless communication system, such as LTE, random access(RA) procedure is used to achieve uplink (UL) time synchronization. RAprocedure is used in LTE during initial access, handover, radio resourcecontrol (RRC) connection re-establishment procedure, positioningpurpose, scheduling request transmission, secondary cell group (SCG)addition/modification and data or control information transmission in ULby non-synchronized user equipment (UE) in RRC_CONNECTED state. In LTEtwo types of RA procedure are defined: contention-based andcontention-free.

A procedure for idle to connected state transition usingcontention-based RA (CBRA) procedure leads to a total delay of 29.5transmit time intervals (TTIs). However, for the next generation radioaccess technology the idle to connected transition delay requirement is10 ms. Therefore, a need exits for enhancing the CBRA procedure.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a communication method and system forconverging a fifth generation (5G) communication system for supportinghigher data rates beyond a fourth generation (4G) system.

In accordance with an aspect of the present disclosure, a method of auser equipment (UE) for performing a random access (RA) procedure isprovided. The method includes transmitting a first message including aRA preamble and a UE identifier (ID) to a base station (BS), andreceiving a second message including a sequence index of the RA preamblefrom the BS.

In accordance with another aspect of the present disclosure, a UE forperforming a RA procedure is provided. The UE includes a transceiver anda controller. The transceiver is configured to receive signals from aBS, and transmit signals to the BS. The controller is configured tocontrol the transceiver to transmit a first message including a RApreamble and a UE ID to the BS, and control the transceiver to receive asecond message including a sequence index of the RA preamble from theBS.

In accordance with another aspect of the present disclosure, a method ofa BS for performing a RA procedure is provided. The method includesreceiving a first message including a RA preamble and a UE ID from a UE,and transmitting a second message including a sequence index of the RApreamble to the UE.

In accordance with another aspect of the present disclosure, a BS forperforming a RA procedure is provided. The BS includes a transceiver anda controller. The transceiver is configured to receive signals from aUE, and transmit signals to the UE. The controller is configured tocontrol to the transceiver to receive a first message including a RApreamble and a UE ID from the UE, and control to the transceiver totransmit a second message including a sequence index of the RA preambleto the UE.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a contention-based random access (CBRA) procedure;

FIG. 2 illustrates a contention-free random access (CFRA) procedure;

FIG. 3 illustrates a procedure for idle to connected state transitionusing a CBRA procedure;

FIG. 4 illustrates a two-step contention based random access (RA)procedure according to an embodiment of the present disclosure;

FIG. 5 illustrates an alternative two-step contention based RA procedureaccording to an embodiment of the present disclosure;

FIGS. 6A and 6B illustrate enhanced physical random access channel(PRACH) slot/resource formats for performing a two-step RA procedureaccording to various embodiments of the present disclosure;

FIG. 6C illustrates an enhanced PRACH slot/resource format forperforming a two-step RA procedure according to an embodiment of thepresent disclosure;

FIG. 6D illustrates an enhanced PRACH slot/resource format forperforming a two-step RA procedure according to an embodiment of thepresent disclosure;

FIG. 6E illustrates an enhanced PRACH slot/resource format forperforming a two-step RA procedure according to an embodiment of thepresent disclosure;

FIG. 7 illustrates a two-step to four-step fall back method for a RAaccording to an embodiment of the present disclosure;

FIG. 8 illustrates an two-step to four-step fall back method for a RAaccording to an embodiment of the present disclosure;

FIG. 9 illustrates an two-step to four-step fall back method for arandom access according to an embodiment of the present disclosure;

FIG. 10 illustrates an two-step to four-step fall back method for a RAaccording to an embodiment of the present disclosure;

FIG. 11 illustrates an RA procedure when a user equipment (UE) does notreceive an RA response (RAR) after transmitting RA preamble andadditional information according to an embodiment of the presentdisclosure;

FIG. 12 is a block diagram of a UE for performing an RA procedureaccording to an embodiment of the present disclosure; and

FIG. 13 is a block diagram of a base station (BS) for performing an RAprocedure according to an embodiment of the present disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

It is known to those skilled in the art that blocks of a flowchart (orsequence diagram) and a combination of flowcharts may be represented andexecuted by computer program instructions. These computer programinstructions may be loaded on a processor of a general purpose computer,special purpose computer, or programmable data processing equipment.When the loaded program instructions are executed by the processor, theycreate a means for carrying out functions described in the flowchart.Because the computer program instructions may be stored in a computerreadable memory that is usable in a specialized computer or aprogrammable data processing equipment, it is also possible to createarticles of manufacture that carry out functions described in theflowchart. Because the computer program instructions may be loaded on acomputer or a programmable data processing equipment, when executed asprocesses, they may carry out steps of functions described in theflowchart.

A block of a flowchart may correspond to a module, a segment, or a codecontaining one or more executable instructions implementing one or morelogical functions, or may correspond to a part thereof. In some cases,functions described by blocks may be executed in an order different fromthe listed order. For example, two blocks listed in sequence may beexecuted at the same time or executed in reverse order.

In this description, the words “unit”, “module” or the like may refer toa software component or hardware component, such as, for example, afield-programmable gate array (FPGA) or an application-specificintegrated circuit (ASIC) capable of carrying out a function or anoperation. However, a “unit”, or the like, is not limited to hardware orsoftware. A unit, or the like, may be configured so as to reside in anaddressable storage medium or to drive one or more processors. Units, orthe like, may refer to software components, object-oriented softwarecomponents, class components, task components, processes, functions,attributes, procedures, subroutines, program code segments, drivers,firmware, microcode, circuits, data, databases, data structures, tables,arrays or variables. A function provided by a component and unit may bea combination of smaller components and units, and may be combined withothers to compose larger components and units. Components and units maybe configured to drive a device or one or more processors in a securemultimedia card.

FIG. 1 illustrates a contention-based random access (CBRA) procedure.

Referring to FIG. 1, a user equipment (UE) transmits a random access(RA) preamble to evolved node B (eNB) at operation 110.

The UE selects one of the available 64-Ncf contention based RApreambles. Ncf is the number of RA preambles reserved for contentionfree access. The contention based RA preambles can be optionallypartitioned into two groups. If two groups are configured, the UEselects the group based on size of a message (i.e., MSG3) that the UEcan transmit at operation 130. The initial RA preamble transmissionpower is set based on open loop estimation after compensating for pathloss.

The ENB transmits a RA response (RAR) on physical downlink sharedchannel (PDSCH) addressed to RA-radio network temporary identifier(RA-RNTI) to the UE at operation 120.

The RA-RNTI identifies the time-frequency slot in which RA preamble wasdetected by eNB. RAR conveys RA preamble identifier (ID), timingalignment information, temporary cell-radio network temporary identifier(C-RNTI) and uplink (UL) grant for a message (i.e., MSG3) to betransmitted at operation 130. RAR may also include back off indicator toinstruct the UE to back off for period of time before retrying RAattempt. RAR is transmitted in RAR window. RAR window starts at subframe‘x+3’ for RA preamble transmitted in subframe ‘x’. RAR window size isconfigurable.

The UE performs scheduled UL transmission on UL shared channel (UL SCH)at operation 130.

A message, such as RRC Connection Request, RRC ConnectionRe-establishment request, RRC handover confirm, scheduling request, andthe like, may be transmitted at operation 130. The message transmittedat operation 130 is commonly referred as MSG3. The message transmittedat operation 130 may include the UE identity, such as C-RNTI or systemarchitecture evolution (SAE)-temporary mobile subscriber identity(S-TMSI) or a random number. Hybrid automatic repeat request (HARQ) isused for the scheduled UL transmission.

The ENB transmits a contention resolution message at operation 140.

HARQ is used for transmission of a contention resolution message. Acontention resolution message is addressed to C-RNTI (if C-RNTI isincluded in MSG3) or temporary C-RNTI (if the UE identity is included inMSG3). On successful decoding of the contention resolution message, HARQfeedback is only sent by the UE which detects its own UE ID (or C-RNTI).

FIG. 2 illustrates a contention-free RA (CFRA) procedure.

Referring to FIG. 2, contention free RA procedure is used for scenarios,such as handover where low latency is required, timing advanceestablishment for secondary cell (Scell), and the like.

The ENB assigns to the UE non-contention RA preamble in dedicatedsignaling at operation 210.

The UE transmits the assigned non-contention RA preamble at operation220.

The ENB transmits the RAR on PDSCH addressed to RA-RNTI at operation230. RAR conveys RA preamble ID and timing alignment information. RARmay also include UL grant. RAR is transmitted in RAR window similar tocontention based RA procedure. Contention free RA procedure terminatesafter receiving the RAR.

FIG. 3 illustrates a procedure for idle to connected state transitionusing a CBRA procedure.

Referring to FIG. 3, the UE transmits an RA preamble to the eNB atoperation 310, the eNB transmits a RAR on PDSCH addressed to RA-RNTI tothe UE at operation 320, and the UE performs scheduled UL transmissionon UL SCH at operation 330, similar to the CBRA procedure illustratedFIG. 1. The scheduled transmission in operation 330, i.e., MSG3 mayrefer to a connection request or a connection resume request.

The ENB transmits a contention resolution message at operation 340. Thecontention resolution message in operation 340 of FIG. 3 may refer to aconnection setup (if a connection request is received at operation 330)or a connection resume (if a connection resume request is received atoperation 330).

The UE performs scheduled transmission at operation 350. The scheduledtransmission in operation 350 may refer to a connection setup complete(if a connection setup is received at operation 340) or a connectionresume complete (if a connection resume is received at operation 340).

Meanwhile, the CBRA procedure leads to a total delay of 29.5 transmittime intervals (TTIs) as shown in Table 1 below.

TABLE 1 Delay Calculation* Average delay due to RACH scheduling period(1 ms RACH 0.5 cycle) Transmission of RACH Preamble 1 Preamble detectionand transmission of RA response (Time 3 between the end RACHtransmission and UE's reception of scheduling grant and timingadjustment) UE Processing Delay (decoding of scheduling grant, timing 5alignment and C-RNTI assignment + L1 encoding of RRC Connection Request)Transmission of MSG 3 1 Processing delay in eNB 4 Transmission of MSG4 1Processing delay in UE 12 Transmission of MSG 5 1

For the next generation radio access technology the idle to connectedtransition delay requirement is 10 ms. So there is need to enhance theCBRA procedure.

FIG. 4 illustrates a two-step contention based RA procedure according toan embodiment of the present disclosure. In the procedure illustrated inFIG. 4, contention resolution is performed in two steps.

Referring to FIG. 4, the UE transmits a RA channel (RACH) preamble and aUE ID to a base station (BS) (e.g., node B (NB), eNB, or gNB) atoperation 410. RACH preamble and UE ID can be transmitted in a singlephysical layer protocol data unit (PDU) or separate physical layer PDUs.The RACH preamble and the UE ID at operation 410 can be sent by UE insame time slot or different time slots. The operation 410 oftransmitting RACH preamble and UE ID can be referred as MSG1transmission. The UE ID can be at least one of Random ID, S-TMSI,C-RNTI, Resume ID, IMSI, idle mode ID, Inactive Mode ID, and the like.The UE ID can be different in different scenarios in which the UEperforms the RA procedure. When the UE performs RA after power on (i.e.,before the UE is attached to the network), the UE ID can be a random ID.Meanwhile, the UE may have a previously assigned or predetermined UE ID.For example, when the UE perform RA in IDLE state after the UE isattached the network the UE can use a previously assigned S-TMSI as theUE ID. If UE has an assigned C-RNTI (e.g., in connected state) the UEcan use the C-RNTI as the UE ID. In case the UE is in INACTIVE state,the UE can use a resume ID as the UE ID.

NB determines whether NB has received the RACH preamble and the UE ID atoperation 415.

If the NB has received both the RACH preamble and the UE ID, NB sends aRAR (also referred as MSG2) to the UE at operation 420. The RAR includeat least one of timing advanced (TA), RACH preamble ID (RAPID) or the UEID. The RAPID may refer to information on the received RACH preamble,e.g., a sequence index of the received RACH preamble. UE ID included inRAR is the UE ID received from UE. C-RNTI (or temporary C-RNTI) can beadditionally included in RAR if the UE ID received from UE is notC-RNTI. Grant for UL transmission may also be included.

If physical downlink control channel (PDCCH) scheduling RAR is addressedto RA-RNTI corresponding to UE's RACH preamble transmitted at operation410, RAPID received in RAR at operation 420 corresponds to UE's RACHpreamble transmitted in operation 410, and the UE ID included in RAR isthe UE ID transmitted by UE at operation 410, then the UE considerscontention resolution as successful. Note that RA-RNTI is used to maskcyclic redundancy check (CRC) of PDCCH which schedules the RAR message.The RA-RNTI is specific to time and/or frequency resource in which RACHpreamble is transmitted. The RAR message may include a RAPID.

FIG. 5 illustrates an alternative two-step contention based RA procedureaccording to an embodiment of the present disclosure

Referring to FIG. 5, the two-step contention based RA procedureillustrated in FIG. 5 is similar to that illustrated in FIG. 4 exceptthat in addition to the UE ID some additional control information can besent in operation 510. In other words, the UE transmits a RACH preamble,a UE ID, and control information to NB at operation 510. RACH preamble,UE ID and control information can be transmitted in a single physicallayer PDU or separate physical layer PDUs. The RACH preamble, the UE IDand the control information at operation 510 can be sent by UE in sametime slot or different time slots. The operation 510 of transmittingRACH preamble, UE ID and control information can also be referred asMSG1 transmission. The control information may include one or more ofconnection request indication, connection resume request indication,system information (SI) request indication, bitmap wherein each bit ismapped to SI message or system information block (SIB) requested by UE,buffer status indication, beam information (e.g., one or more DL TX beamID(s)), data indicator, cell/BS/transmission reception point (TRP)switching indication, or connection re-establishment indication, and thelike. Note that any other control information is not precluded.

NB determines whether NB has received the RACH preamble, the UE ID andcontrol information at operation 515.

If RACH preamble, UE ID and control information is received, NB sends aRAR to the UE at operation 520. In addition, NB may transmit a controlmessage based on the control information received at operation 510. Inother words, NB may respond with a control message in addition to RARmessage at operation 525. The control message may depend on controlinformation received at operation 510. The RAR at operation 520 and thecontrol message at operation 525 can be sent by NB in same time slot ordifferent time slot.

Network can signal in dedicated or broadcast signaling the events orservices for which UE should use two-step contention based random accessprocedure.

FIGS. 6A and 6B illustrate enhanced PRACH slot/resource formats forperforming a two-step RA procedure according to various embodiments ofthe present disclosure.

Referring to FIGS. 6A and 6B, in a PRACH slot, the UE performs a PRACHtransmission in a PRACH resource (e.g., R1 of FIG. 6A). In other words,the UE transmits a RA preamble in a PRACH resource on PRACH at firststep of a two-step RA procedure (e.g., operation 410 of FIG. 4,operation 510 of FIG. 5). The PRACH format (i.e., RA preamble) forperforming the PRACH transmission according to an embodiment of thepresent disclosure may include cyclic prefix (CP), PRACH preamblesequence, additional information (i.e., the UE ID, data, controlinformation, CRC, and the like) and guard time (GT). In the system,there can be several PRACH formats wherein all PRACH format may notinclude additional information (i.e., the UE ID, data, controlinformation, CRC, and the like) The PRACH format indicator in PRACHconfiguration may indicate the PRACH format to be used for PRACHconfiguration. In an embodiment of the present disclosure, NB mayconfigure multiple PRACH configurations having PRACH formats whichinclude additional information (i.e., the UE ID, data, controlinformation, CRC, and the like) and which do not include additionalinformation. The UE may choose PRACH configuration based onservice/slice in which the UE is interested. For example, forultra-reliable low latency (URLL) slice/service, the UE may use PRACHconfiguration which allows transmitting additional information. NB mayalso indicate which PRACH format to be used for which service/slice.

FIG. 6C illustrates an enhanced PRACH slot/resource format forperforming a two-step RA procedure according to an embodiment of thepresent disclosure.

Referring to FIG. 6C, PRACH sequence and additional information (i.e.,the UE ID, data, control information, CRC, and the like) are frequencydivision multiplexed in PRACH resources. PRACH format of FIG. 6Crequires more resources because of additional CP and GT compared toPRACH format of FIG. 6A. However, duration of a slot of PRACH format ofFIG. 6C is shorter, compared to that of FIG. 6B, which is beneficial inreducing latency.

FIG. 6D illustrates an enhanced PRACH slot/resource format forperforming a two-step RA procedure according to an embodiment of thepresent disclosure.

Referring to FIG. 6D, PRACH sequence and additional information (i.e.,the UE ID, data, control information, CRC, and the like) are frequencydivision multiplexed in PRACH resource, similar to a PRACH formatillustrated FIG. 6C. Furthermore, resource R1 for a PRACH sequence andresource R3 for additional information are separated. The PRACHconfiguration indicates resources for a PRACH sequence (i.e., PRACHresources) as well as resources for additional information. Mappingbetween resources for a PRACH sequence and resources for additionalinformation can be implicit (e.g., first resource for a PRACH sequencemaps to first resource for additional information, and so on) or can beexplicitly indicated. For example, first resource is for a PRACHpreamble and then next N (N can be 1) resource(s) is for additionalinformation, and so on. Since all UEs performing RA may not have totransmit additional information, separating resources for a PRACHpreamble and resources for additional information can reduce contentionon the resources for the additional information. There can be one to onemapping or one to many mapping between resources for a PRACH preambleand resource for additional information. In an embodiment of the presentdisclosure, only resources for a PRACH preamble are indicated, andresources for additional information can be pre-defined.

FIG. 6E illustrates an enhanced PRACH slot/resource format forperforming a two-step RA procedure according to an embodiment of thepresent disclosure.

Referring to FIG. 6E, PRACH sequence and additional information (i.e.,the UE ID, data, control information, CRC, and the like) are timedivision multiplexed. In other words, a slot for PRACH sequence (i.e.,PRACH slot) and a slot for additional information (i.e., data slot) aredifferent. A PRACH slot and a data slot may or may not be consecutive.

Meanwhile, it is possible that NB can only receive PRACH preamble andcannot decode additional information (i.e., the UE ID, data, controlinformation, and the like) successfully. In an embodiment of the presentdisclosure, NB may not send RAR if only PRACH preamble is received andadditional information is not received. But this is not efficient as theUE will again send RA preamble which leads to more delay. Therefore, incase only PRACH preamble is received and additional information is notsuccessfully decoded, a two-step RA procedure may fall back to afour-step RA procedure according to an embodiment of the presentdisclosure. In the two-step to four-step fall back method, if only PRACHpreamble is received and additional information cannot be successfullydecoded, NB sends RAR including TA and RAPID. Temporary C-RNTI may alsobe included in the RAR. In addition, the RAR may include an indicationthat additional information is not decoded. NB may indicate thatadditional information is not decoded implicitly. For example, NB maytransmit RAR without the UE ID and the absence of the UE ID in RAR mayimplicitly indicate that NB has only received RACH preamble.Alternatively, NB may indicate that additional information is notdecoded explicitly. For example, NB may transmit one bit indication inRAR to indicate that only RACH preamble is received and additionalinformation (e.g. UE ID) is not received.

FIG. 7 illustrates a two-step to four-step fall back method for a RAaccording to an embodiment of the present disclosure.

If the UE ID transmitted by UE to NB in MSG1 is not included in RAR(i.e., implicitly indicated) or there is an explicit indication in RARthat additional information (i.e., the UE ID, data, control information,and the like) is not decoded by NB, the UE falls back to a four-step RAprocedure as shown in FIG. 7.

Referring to FIG. 7, the UE transmits MSG1 including RA preamble andadditional information (i.e., the UE ID) to NB at operation 710.Additional information may also include data and control information.

If MSG1 is received, NB tries decoding additional information. If theadditional information is successfully decoded, NB sends MSG2 (i.e.,RAR) including the UE ID, as illustrated in FIGS. 4 and 5. If theadditional information is not successfully decoded, NB sends RARincluding UL grant. RAR also includes TA and RAPID. Temporary C-RNTI mayalso be included in the RAR.

If RAR corresponding to the UE's transmitted RA preamble is received,the UE determines whether RAR includes the UE ID at operation 720.Alternatively, the UE may determine whether RAR includes an indicationthat additional information (e.g., the UE ID) is received by NB. If RARincludes the UE ID or indicates that additional information is received,contention resolution is successful at operation 730 (i.e., two-step RAprocedure END). Otherwise, the UE falls back to four-step procedure,i.e., the UE transmits MSG3 including at least the UE ID using theallocated grant at operation 740. Other information such as connectionrequest or connection resume request or SI request and the like can alsobe transmitted in MSG3.

After transmitting MSG3, the UE waits for MSG4 for pre-defined time atoperation 750. If MSG4 is received, the UE determines whether MSG4includes the UE ID transmitted in MSG3 at operation 760. If MSG4includes the UE ID, contention resolution is successful at operation 770(i.e., four-step fall back RA procedure END). If MSG4 including UE IDtransmitted in MSG3 is not received for pre-defined time UE retransmitsMSG1.

FIG. 8 illustrates a two-step to four-step fall back method for a RAaccording to an embodiment of the present disclosure.

Referring to FIG. 8, similar to a two-step to four-step fall back methodof FIG. 7, if the UE ID is not included in RAR (i.e., implicitlyindicated) or there is an explicit indication in RAR that additionalinformation (i.e., the UE ID, data, control information, and the like)is not decoded by NB, the UE falls back to a four-step RA procedure asshown in FIG. 8.

Specifically, similar to the method of FIG. 7, the UE transmits MSG1including RA preamble and additional information (i.e., the UE ID, data,control information, and the like) to NB at operation 810. If MSG1 isreceived, NB tries decoding additional information. If the additionalinformation is successfully decoded, NB sends MSG2 (i.e., RAR) includingthe UE ID, as illustrated in FIGS. 4 and 5. If the additionalinformation is not successfully decoded, NB may determine whether toinclude grant in RAR. In other words, contrary to the method of FIG. 7,grant is not always included in RAR. If NB wants the UE to fall back tofour-step procedure, NB includes grant in MSG2, otherwise NB does notinclude grant in RAR. RAR also includes TA and RAPID. Temporary C-RNTImay also be included in the RAR.

If RAR corresponding to the UE's transmitted RA preamble is received,the UE determines whether RAR includes the UE ID at operation 820.Alternatively, the UE may determine whether RAR includes an indicationthat additional information (e.g., the UE ID) is received by NB. If RARincludes the UE ID or indicates that additional information is received,contention resolution is successful at operation 830 (i.e., two-step RAprocedure END).

If the UE ID is not included in RAR or there is an explicit indicationin RAR that additional information (i.e., the UE ID, data, controlinformation, and the like) is not decoded by NB, the UE determineswhether grant is received in RAR at operation 835. If grant is notreceived in RAR, the UE retransmits RA preamble and the UE ID. If grantis received in RAR, the UE falls back to four-step procedure i.e., theUE transmits MSG3 including the UE ID using the allocated grant atoperation 840. Other information such as connection request orconnection resume request or SI request and the like can also betransmitted in MSG3.

After transmitting MSG3, the UE waits for MSG4 for pre-defined time atoperation 850. If MSG4 is received, the UE determines whether MSG4includes the UE ID transmitted in MSG3 at operation 860. If MSG4includes the UE ID, contention resolution is successful at operation 870(i.e., four-step fall back RA procedure END). If MSG4 including UE IDtransmitted in MSG3 is not received for pre-defined time UE retransmitsMSG1.

FIG. 9 illustrates a two-step to four-step fall back method for an RAaccording to an embodiment of the present disclosure.

Referring to FIG. 9, similar to a two-step to four-step fall backmethods of FIGS. 7 and 8, if the UE ID is not included in RAR (i.e.,implicitly indicated) or there is an explicit indication in RAR thatadditional information (i.e., the UE ID, data, control information, andthe like) is not decoded by NB, the UE falls back to a four-step RAprocedure as shown in FIG. 9.

Specifically, similar to the methods of FIGS. 7 and 8, the UE transmitsMSG1 including RA preamble and additional information (i.e., the UE ID,data, control information, and the like) to NB at operation 910. If MSG1is received, NB tries decoding additional information. If the additionalinformation is successfully decoded, NB sends MSG2 (i.e., RAR) includingthe UE ID, as illustrated in FIGS. 4 and 5. If the additionalinformation is not successfully decoded, NB may determine whether toinclude grant in RAR. In other words, contrary to the method of FIG. 7,grant is not always included in RAR. Similar to the method of FIG. 8, ifNB wants the UE to fall back to four-step procedure, NB includes grantin MSG2, otherwise NB does not include grant in RAR. In addition, NB maydetermine whether to include an indication to transmit the UE ID in RAR.

If RAR corresponding to the UE's transmitted RA preamble is received,the UE determines whether RAR includes the UE ID at operation 920.Alternatively, the UE may determine whether RAR includes an indicationthat additional information (e.g., the UE ID) is received by NB. If RARincludes the UE ID or indicates that additional information is received,contention resolution is successful at operation 930 (i.e., two-step RAprocedure END). If the UE ID is not included in RAR or there is anexplicit indication in RAR that additional information (i.e., the UE ID,data, control information, and the like) is not decoded by NB, the UEdetermines whether grant is received in RAR at operation 935. If grantis received in RAR, the UE falls backs to 4 step procedure i.e., the UEtransmits MSG3 including the UE ID using the allocated grant atoperation 940. Other information such as connection request orconnection resume request or SI request and the like can also betransmitted in MSG3. After transmitting MSG3, the UE waits for MSG4 forpre-defined time at operation 950. If MSG4 is received, the UEdetermines whether MSG4 includes the UE ID transmitted in MSG3 atoperation 960. If MSG4 includes the UE ID, contention resolution issuccessful at operation 970 (i.e., four-step fall back RA procedureEND). If MSG4 including UE ID transmitted in MSG3 is not received forpre-defined time, the UE retransmits MSG1.

If grant is not received in RAR, the UE retransmits RA preamble. Inaddition, the UE may retransmit additional information (i.e., the UE ID,data, control information, and the like) while transmitting RA preamblebased on indication from NB. Specifically, the UE may determine whetherRAR includes indication to transmit additional information at operation937. If RAR includes the indication, the UE retransmits MSG1 includingboth RA preamble and additional information, otherwise the UEretransmits MSG1 only including RA preamble at operation 939.

FIG. 10 illustrates a two-step to four-step fall back method for a RAaccording to an embodiment of the present disclosure.

Referring to FIG. 10, similar to a two-step to four-step fall backmethods of FIGS. 7, 8 and 9, if the UE ID is not included in RAR (i.e.,implicitly indicated) or there is an explicit indication in RAR thatadditional information (i.e., the UE ID, data, control information, andthe like) is not decoded by NB, the UE falls back to a four-step RAprocedure as shown in FIG. 10.

Specifically, similar to the methods of FIGS. 7, 8, and 9, the UEtransmits MSG1 including RA preamble and additional information (i.e.,the UE ID, data, control information, and the like) to NB at operation1010. If MSG1 is received, the NB tries decoding additional information.If the additional information is successfully decoded, NB sends MSG2(i.e., RAR) including the UE ID, as illustrated in FIGS. 4 and 5. If theadditional information is not successfully decoded, the NB may determinewhether to include grant in RAR. In other words, contrary to the methodof FIG. 7, grant is not always included in RAR. Similar to the methodsof FIGS. 8 and 9, if NB wants the UE to fall back to four-stepprocedure, NB includes grant in MSG2, otherwise NB does not includegrant in RAR.

If RAR corresponding to UE's transmitted PA preamble is received, the UEdetermines whether RAR includes the UE ID at operation 1020.Alternatively, the UE may determine whether RAR includes an indicationthat additional information (e.g., the UE ID) is received by NB. If RARincludes the UE ID or indicates that additional information is received,contention resolution is successful at operation 1030 (i.e., two-step RAprocedure END). If the UE ID is not included in RAR or there is anexplicit indication in RAR that additional information (i.e., the UE ID,data, control information, and the like) is not decoded by NB, the UEdetermines whether grant is received in RAR at operation 1035. If grantis received in RAR, the UE falls backs to 4 step procedure i.e., the UEtransmits MSG3 including the UE ID using the allocated grant atoperation 1040. Other information such as connection request orconnection resume request or SI request and the like can also betransmitted in MSG3. After transmitting MSG3, the UE waits for MSG4 forpre-defined time at operation 1050. If MSG4 is received, the UEdetermines whether MSG4 includes the UE ID transmitted in MSG3 atoperation 1060. If MSG4 includes the UE ID, contention resolution issuccessful at operation 1070 (i.e., four-step fall back RA procedureEND). If MSG4 including UE ID transmitted in MSG3 is not received forpre-defined time UE retransmits MSG1.

If grant is not received in RAR, the UE retransmits RA preamble. Inaddition, the UE may retransmit additional information (i.e., the UE ID,data, control information, and the like) while transmitting RA preamblebased on parameter ‘N,’ where parameter ‘N’ indicates the number oftimes the UE can retransmit additional information (i.e., the UE ID,data, control information, and the like) along with RA preamble.Specifically, the UE may determine whether the UE has transmitted RApreamble with the UE ID ‘N’ times at operation 1037. If the UE hastransmitted RA preamble with the UE ID more than ‘N’ times, the UEretransmits MSG1 only including RA preamble at operation 1039. Parameter‘N’ can be pre-defined or indicated by network in broadcast or dedicatedsignaling. Alternatively, parameter ‘N’ can be signaled along with PRACHconfiguration.

FIG. 11 illustrates an RA procedure when a UE does not receive a RARafter transmitting an RA preamble and additional information accordingto an embodiment of the present disclosure.

Referring to FIG. 11, if the UE does not receive RAR after transmittingMSG1 including RA preamble and additional information (i.e., the UE ID,data, control information, and the like), then in an embodiment of thepresent disclosure, the UE may retransmit MSG1 including RA preamble andadditional information. In an alternate embodiment of the presentdisclosure, the UE may determine whether to retransmit additionalinformation along with RA preamble or not. The UE can determine whetherto retransmit additional information along with RA preamble based onparameter ‘N,’ where parameter ‘N’ indicates the number of times the UEcan retransmit additional information along with RACH preamble.Parameter ‘N’ can be pre-defined or indicated by network in broadcast ordedicated signaling. Alternatively, parameter ‘N’ can be signaled alongwith PRACH configuration.

Referring to FIG. 11, the UE transmits MSG1 including RA preamble andadditional information (i.e., the UE ID, data, control information, andthe like) to NB at operation 1110. If nothing is received by NB, the NBdoes not transmit RAR to UE, and the UE cannot receive RAR. Therefore,the UE retransmits MSG1 including RA preamble and additional informationto NB at operation 1120. Meanwhile, if the UE retransmits MSG1 includingRA preamble and additional information several times but RAR is notreceived, the UE may determine whether to retransmit additionalinformation along with RA preamble to NB at operation 1130. For example,the UE may determine whether to retransmit additional information alongwith RA preamble based on parameter ‘N,’ where parameter ‘N’ indicatesthe number of times the UE can retransmit additional information. Basedon the determination, the UE may retransmit only RACH preamble, or bothRACH preamble and additional information to the NB at operation 1140.

FIG. 12 is a block diagram of a UE for performing an RA procedureaccording to an embodiment of the present disclosure.

Referring to FIG. 12, the UE include a transceiver (1210), a controller(1220) and a memory (1230). The controller (1220) may refer to acircuitry, an application-specific integrated circuit (ASIC), or atleast one processor. The transceiver (1210), the controller (1220) andthe memory (1230) are configured to perform the operations of the UE inthe RA procedure illustrated in FIGS. 4, 5, and 7 to 11 or describedabove. For example, the transceiver (1210) is configured to receivesignals from a BS and transmit signals to the BS. The controller (1220)may be configured to control the transceiver (1210) to transmit a firstmessage including a RA preamble and a UE ID to the BS, and control thetransceiver (1210) to receive a second message including a sequenceindex of the RA preamble from the BS.

FIG. 13 is a block diagram of a BS for performing an RA procedureaccording to an embodiment of the present disclosure.

Referring to FIG. 13, the BS includes a transceiver (1310), a controller(1320) and a memory (1330). The controller (1320) may refer to acircuitry, an ASIC, or at least one processor. The transceiver (1310),the controller (1320) and the memory (1330) are configured to performthe operations of NB in the RA procedure illustrated in FIGS. 4, 5, and7 to 11 or described above. For example, the transceiver (1310) isconfigured to receive signals from a UE, and transmit signals to the UE.The controller (1320) may be configured to control the transceiver(1310) to receive a first message including a RA preamble and a UE IDfrom the UE, and control the transceiver (1310) to transmit a secondmessage including a sequence index of the RA preamble to the UE.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of a user equipment (UE) for performinga random access (RA) procedure, the method comprising: transmitting afirst message including a RA preamble and a UE identifier (ID) to a basestation (BS); and receiving a second message including a sequence indexof the RA preamble from the BS.
 2. The method of claim 1, furthercomprising: receiving a control message based on the control informationfrom the BS, wherein the first message further includes controlinformation.
 3. The method of claim 1, wherein the RA preamble and theUE ID are frequency or time division multiplexed in radio resources fortransmitting the first message.
 4. The method of claim 3, whereinresources for the RA preamble and resources for the UE ID are separatedin the radio resources.
 5. The method of claim 1, further comprising:determining whether the second message includes the UE ID transmitted inthe first message; and if the second message does not include the UE IDtransmitted in the first message, transmitting a third message includingthe UE ID to the BS.
 6. The method of claim 5, further comprising:determining whether the second message includes grant for transmittingthe third message; and if the second message does not include the grant,retransmitting the first message to the BS.
 7. The method of claim 6,wherein the retransmitting of the first message is further comprising:determining whether the second message includes indication to transmitthe UE ID, wherein the first message is retransmitted if the secondmessage includes the indication, and a message including the RA preambleis transmitted if the second message does not include the indication tothe BS.
 8. The method of claim 6, further comprising: determiningwhether the UE ID has been transmitted along with the RA preamble morethan a predefined number of times; and if the UE ID has been transmittedalong with the RA preamble more than the predefined number of times,transmitting a message including the RA preamble to the BS.
 9. A userequipment (UE) comprising: a transceiver configured to: receive signalsfrom a base station (BS), and transmit signals to the BS; and at leastone processor configured to: control the transceiver to transmit a firstmessage including a random access (RA) preamble and a UE identifier (ID)to the BS, and control the transceiver to receive a second messageincluding a sequence index of the RA preamble from the BS.
 10. The UE ofclaim 9, wherein the at least one processor is further configured tocontrol the transceiver to receive a control message based on thecontrol information, and wherein the first message further includescontrol information.
 11. The UE of claim 9, wherein the RA preamble andthe UE ID are frequency or time division multiplexed in resources fortransmitting the first message.
 12. The UE of claim 9, wherein the atleast one processor is further configured to: determine whether thesecond message includes the UE ID transmitted in the first message, andif the second message does not include the UE ID transmitted in thefirst message, control the transceiver to transmit a third messageincluding the UE ID to the BS.
 13. The UE of claim 12, wherein the atleast one processor is further configured to: determine whether thesecond message includes grant for transmitting the third message, and ifthe second message does not include the grant, retransmit the firstmessage to the BS.
 14. A method of a base station (BS) for performing arandom access (RA) procedure, the method comprising: receiving a firstmessage including a RA preamble and a user equipment (UE) identifier(ID) from a UE; and transmitting a second message including a sequenceindex of the RA preamble to the UE.
 15. The method of claim 14, furthercomprising: transmitting a control message based on the controlinformation to the UE, wherein the first message further includescontrol information.
 16. The method of claim 14, further comprising:determining whether the UE ID is decoded successfully; and determiningwhether to transmit the UE ID in the second message, wherein if the UEID is successfully decoded, the UE ID is transmitted in the secondmessage.
 17. The method of claim 16, further comprising: if the UE ID isnot successfully decoded, determining whether to include grant in thesecond message, wherein the grant is used for retransmitting the UE ID.18. A base station (BS) for performing a random access (RA) procedure,the BS comprising: a transceiver configured to: receive signals from auser equipment (UE), and transmit signals to the UE; and at least oneprocessor configured to: control to the transceiver to receive a firstmessage including a RA preamble and a UE identifier (ID) from the UE,and control to the transceiver to transmit a second message including asequence index of the RA preamble to the UE.
 19. The BS of claim 18,wherein the at least one processor is further configured to: determinewhether to decode the UE ID successfully, and determine whether totransmit the UE ID in the second message, wherein if the UE ID issuccessfully decoded, the UE ID is transmitted in the second message.20. The BS of claim 19, wherein the at least one processor is furtherconfigured to: if the UE ID is not successfully decoded, determinewhether to include grant in the second message, wherein the grant isused for retransmitting the UE ID.